The present invention relates generally to cutting devices, and more particularly to devices useful for cutting rigid plastics foams.
It is well known that certain rigid plastics foams, such as polystyrene may readily be cut with heated wires. These wires are heated to a temperature above the fusion temperature of the plastics material, and are passed through a body of the material in a direction which may be perpendicular to their longitudinal axes.
Conventional hot wire techniques as described in the previous paragraph make little impression upon certain foam plastics materials such as polyurethane foam (especially "self-extinguishing" polyurethane foam) and poly-isocyanurate.
In U.S. Pat. No. 3,786,701, issued to Eugene A. Ludwig, a modified hot wire cutting device has been described which is claimed to be useful for cutting polyurethane foam and like. According to the Ludwig patent, a conventional hot wire cutting device is modified by oscillating the entire cutting assembly, upon which the heated wires are mounted, transversely of the direction of the cut.
As in the conventional hot wire cutting technique, the wires are heated above the fusion temperature of the foam, and the oscillatory action serves to impede the build up of fused resin on the wires.
By this method, the build up of fused plastics material cannot be entirely eliminated. With self-extinguishing polyurethane foam (which incorporates a filler substance which is substantially non-fusable at the temperature of the cutting wire) the problem is increased by the build up on the wire of an insulated layer of filler and insufficiently fused polyurethane which slows up and eventually prevents the thermal cutting action. Another foam plastics material which presents particular problems is poly-isocyanurate. This appears to pyrolize at the wire temperature, leaving a residue of carbonaceous material on the wires.
A further problem inherent in the Ludwig cutter is that the oscillating wires exert lateral forces on the body of material being cut, and tend to shift it sideways. These forces increase as fused or charred material builds up on the wires. To avoid the body shifting sideways, it is necessary to anchor it firmly, or to place weights on the top of it.
Plastics foam materials which cannot be cut by a hot wire have hitherto been cut by conventional sawing methods. For example, polyurethane slabs for insulation purposes are usually cut from a block of rigid foam with a band saw. The cutting operation is time consuming because only one cut may be made at a time. Because the blocks of polyurethane foam which are cut are usually several feet wide, it is impractical to use a saw which cuts with an oscillating movement. Any such oscillating saw would need to have an amplitude of oscillation which exceeded the width of the block, to ensure sufficient clearing of swarf from the cutting region.
Another problem associated with the use of band saws arises from the band like nature of the blade. Any slight deflection of the band (for example through inhomogeneity of the block of material being cut) tends to twist the blade, causing a wavy or rippled cut surface.
It is an object of the present invention to provide an improved method and apparatus for cutting foamed plastics materials, including those which cannot be cut by conventional hot wire techniques.
It is another object of the invention to provide a method and apparatus for making multiple cuts in a block of foamed plastics material, including those materials which cannot be cut by conventional hot wire techniques.
It is a further object of the invention to provide apparatus for cutting polyurethane foams and the like, which apparatus employs a substantially filamentary cutting element, as hereinafter defined.